The present invention relates to medical procedures performed with the aid of imaging devices. Some aspects of the present invention relate to medical procedures in which two or more images of different imaging modalities and which are taken simultaneously and/or at different times are used. Other aspects of the present invention relate to the general field known as “Image Guided Surgery”. In particular, the present invention relates to a method and system for displaying cross-sectional images of a body so as to render the cross-sectional images more interpretable by a user.
Image guided surgery is well known in the art. In a system described in U.S. Pat. No. 5,772,594 a trajectory of a needle is shown on a fluoroscope image in purpose to navigate the needle to a target. U.S. Pat. No. 5,383,454 describes a system for indicating the position of a surgical probe within a head on a selected cross-sectional image that is the closest to the probe location. U.S. Pat. No. 5,873,822 teaches a system for registering the position of a surgical tool on a prerecorded image. U.S. Pat. No. 5,902,239 shows an improved registration method of a surgical instrument on CT or MRI image.
Fusion of two different images in context of image guided surgery is also well known in prior art. Superimposition of diagnostic and additional lesser-quality CT images is achieved in, for example, U.S. Pat. No. 4,791,934 by adjusting the spatial position and angular orientation of a synthesized image made from one of the original images until an optimum match to the other image is achieved. Positioning an ultrasound image relative to a tomography image using fiducials to form a combined resulting image is described in U.S. Pat. No. 5,810,007. Similarly, WO 96/25882 allows visualization of a final rendering that combines in a co-registered manner two images taken by different imaging modalities. U.S. Pat. Nos. 5,871,445 and 5,891,034 show means to scan a first image and generate a second scanned image which has the same position relative to reference points so that the generated second scanned image corresponds to the particular first scanned image.
Thus, it is well known to generate and use images derived from two imaging modalities and modify such images as if viewed from the same direction at the same scale. In other words, it is known how to generate and use spatially overlapping or fused images even if taken from different angles by different imaging modalities. However, the prior art fails to teach the generation and use of non-overlapping images having a known angular relation there amongst.
There are an increasing number of medical procedures that are performed by inserting a probe into the body, leading the probe to a desired treatment location within the body and spatially applying the treatment at such location via the probe. Typically, in such medical procedures, the maneuvering of the probe within the body is assisted by imaging. Most often, a fluoroscope or an ultrasound imaging device are used, because such imaging devices enable real-time imaging, so as to assist in maneuvering the probe to an appropriate location within the body.
A fluoroscopic image provides comprehensive details of the hard tissues of the body such as bones. It also provides a two-dimensional projection of a volume under imaging, so that each image point is an integral of tissue densities along a line of projection. Although the fluoroscopic image lacks depth perception, it is the preferred imaging tool for navigating a probe to a destination within the body. That is because good imaging quality is achieved for the probe itself, as well as for the skeletal elements of the body which are used as landmarks for navigating the probe. It also gives the practitioner a fair perspective view of the on-going procedure.
Ultrasound imaging, on the other hand, gives a cross-sectional image through the body. Soft tissues are distinguishable, but the picture is much less intuitive and the practitioner is required to have special interpretation skills. The main advantage, but also disadvantage, of the ultrasound is the flexibility in directing the imaging plane. However, such flexibility makes the image rather difficult to comprehend. In order to understand the content of an ultrasound image, the practitioner first has to identify the location and direction of the image slice in the body, which is achieved by identifying some anatomical landmarks. Usually these are cross-sectionals through familiar internal organs. Most of misinterpretation of ultrasound images results from misunderstanding the orientation of the image plane. Hence, planar ultrasounds are less frequently used in procedures in which intra-body navigation of operative tools is performed.
Three dimensional (3D) models made by mathematical manipulation of a plurality of image planes are also taught by the prior art. The time required for gathering the data and computing the model cause such models to be considered as a form of imaging that is not real-time. Lately, attempts to develop a real-time 3D-ultrasound apparatus show initial success. The output display of such a device is a plurality of parallel images along a chosen axis. Yet, by using ultrasound, direct imaging of a tool inside the body is not straightforward due to artifacts presented in the image by such tools. It should be emphasized that in contrary to fluoroscopy, each element of an ultrasound image, regardless of whether such image is planar or 3D, represents a small volume in space, hence may address to a set of coordinates in some reference of coordinates related to the body.
CT (Computerized Tomography) and MRI (Magnetic Resonance Imaging) are often being used for diagnostic purposes, and less in the course of therapeutic procedures, although some versions known as the “Open MRI” or “Interventional MRI” or TMRI (therapeutic MRI) are designed to be used intra-operatively. CT and MRI are typically very expensive and cumbersome to operate, which further limits their use.
The original output data of CT and MRI is a set of paralleled cross-sectional images. Each image element represents a small volume characteristic of the particular modality, known as a “voxel”. Mathematically it is possible to manipulate the data to produce an image plane that is of a different direction or spatial location from the original cross-sectionals. Another possibility is, using special filtering, to render a 3D model of a particular characteristic of the data such as the vascular system, bones, tumor, cavities, etc.
Since each of the different-imaging modalities identifies different types and characters of tissues, it is of great advantage to use a plurality of imaging modalities simultaneously. In doing so, it is very important to maintain the practitioner's depth perception and interpretation skills at the highest possible level. There is thus a widely recognized need for, and it would be highly advantageous to have a method and system for displaying cross-sectional images of a body so as to render the cross-sectional images more interpretable by a user.